This patent application claims priority under 35 USC xc2xa7119 to commonly assigned German patent applications DE 100 33 070.3, filed Jul. 7, 2000, and DE 100 16 113.8, filed on Mar. 31, 2000.
This invention relates to heat exchangers, and more particularly to radiators of the type used in vehicles.
Many types of engine powered vehicles utilize a heat exchanger, commonly known as a radiator, to dissipate heat from engine coolant fluid to the ambient air. Such radiators often include a radiator core having a plurality of tubes, through which the coolant flows. The tubes are spaced apart from one another by fins which conduct heat away from the tubes, and dissipate the heat to ambient air which is drawn or forced through the fins between the tubes. To facilitate heat transfer and construction of the radiator, the tubes typically have an elongated rectangular cross-section, with long sidewalls extending through the radiator core for contacting the fins, and short end walls joining the two sidewalls of the tubes.
In one venerable construction of such a radiator, the ends of the tubes are fitted into holes in a header plate, and the joint between the outside surface of the tubes and the header plate is sealed by soldering, brazing, or adhesively bonding the outer surface of the tubes to the header plate. A collecting tank is then joined to the header plate in such a manner that the header plate and tank in combination form a fluid tight reservoir or plenum connecting the open ends of the tubes to a common source of coolant fluid. This construction is undesirable because the header plate, and the operation of joining the tubes to the header plate, involve parts and process steps that add cost and reduce reliability. This construction is also undesirable because fluid flowing between the tubes and the reservoir or plenum must make abrupt turns and undergo rapid expansion or contraction.
In another prior radiator construction, the header plate is combined into the collecting tank through the use of a tubular structure for the collecting tank. The ends of the tubes are contoured and formed to fit into slots in the tubular tank structure. The outer surfaces of the tubes are then joined in a fluid tight manner to the tubular tank structure to form a common reservoir or plenum connecting the tubes. While this construction provides improved manufacturability, by combining the header and tank into one part, the transition for fluid flowing between the plenum and the tubes is still more abrupt and torturous than is desirable.
To facilitate fluid flow, the ends of the tubes joining the tubular tank structure have, in some instances, been enlarged by stretching the walls of the tube at the end joining the tubular tank structure. This typically requires the tubes have walls that are undesirably thick, however, so that the walls of the tube at the enlarged end will still have sufficient thickness and strength for reliable service after the wall of the tube is thinned by stretching. The additional wall thickness is undesirable because it inhibits heat transfer, adds weight and cost, and necessitates the use of relatively large corner radii in fabricating the tubes, to avoid cracking of the tube walls during formation of the tubes. The increased corner radii result in larger gaps to be filled during the process of joining the tubes to the tubular tank structure to form a fluid tight construction, thereby making fabrication more difficult and introducing potential points of failure in operation. An example of this construction is disclosed in German Offenlegungsschrift DE 3834822 A1.
In another form of construction, the header plates are eliminated by stretching the end walls of the tubes for a short distance adjacent the end of the tubes to such a degree that the ends of the sidewalls of adjacent tubes extend across the spaces occupied by the fins and into contact with one another. The side wall ends of the adjacent tubes are then joined to one another, to essentially replace the header plates in the first construction described above, and a tank structure is joined to the stretched end walls of the tubes in a fluid tight manner to form the common reservoir or plenum. Such a construction provides advantages by eliminating the need for a separate header plate, and providing a smoother transition for fluid flowing between the tubes and the common plenum, but still suffers from the disadvantages of requiring a thicker tube wall as described above. Examples of this construction are disclosed in German patent application number 195 43 986 A1; German Utility Model No. 1 519 204; and German DE-PS 1 551 448.
What is needed is an improved radiator and method of constructing such an improved radiator that is of essentially xe2x80x9cheaderlessxe2x80x9d construction and avoids the problems described above.
Our invention provides such an improved radiator through the use of a radiator core including tubes having end walls which are bifurcated for a short distance from the end of the tube and having one or both of the sidewalls in the bifurcated segment of the tube formed outward and adapted to contact and be joined in a fluid tight manner with the sidewall of an adjacent tube in the radiator core. A collecting tank has walls extending over the core to a distance beyond the bifurcation of the sidewalls, and joined to the end walls of the tubes in a fluid tight manner, such that the walls of the collecting tank in conjunction with the bifurcated end walls and outwardly formed sidewalls of the tubes define a common fluid plenum providing fluid communication between the tubes and the collecting tank.
Our invention thus eliminates the need for a separate header plate and provides an improved transition for fluid flowing between the collecting tank and the tubes without the need for stretching the end walls of the tubes. In our radiator, the walls of the collecting tank perform the function provided by the stretched end walls of prior radiator structures. The tubes in our radiators can thus have thinner walls for improved heat transfer and reduced cost and weight. We can utilize tighter bend radii without fear of introducing cracks in the corners of the tubes, and facilitate manufacture of the radiator by reducing the size of gaps between the tubes and adjoining structures in prior radiator constructions. We also achieve a direct reduction in weight and material cost because the redundant function provided by the combined thickness of the stretched tube end walls and the walls of the collecting tank or other structure attached to the stretched end walls is eliminated.
In one form of our invention, the tubes are formed by joining together a first and a second tube half which mate at the end walls to form each tube. In some embodiments of this form of our invention, the first and second tube halves are fabricated to form a generally U-shaped cross section, with the outward projecting legs of the U forming part of the end walls and being joined by one of the side walls of the tube. In some forms of our invention, the legs of each tube half are formed by a simple right angle bend from the side wall of that tube half. The ends of the respective legs of the first and second tube halves are then butted together and bonded to form the end walls of the tube. In other forms, the legs of the first and second tube halves include several bends, which are preferably configured in a complimentary fashion so that the legs of the first and second tube halves will engage each other to facilitate fixturing during manufacture.
In some forms of our invention, the ends of the tubes will be formed prior to welding the intersection of the first and second tube halves. The welded and formed tubes are then assembled with the fins in an interleaved fashion, and joined together by a process such as brazing to form a radiator core, to which one or more collecting tanks are subsequently joined to complete fabrication of the radiator.
In other forms of our invention, the tubes, or the tube halves, the fins, and one or more collecting tanks are assembled in a braze fixture and simultaneously brazed together in a single operation.
In some embodiments of our invention, only one sidewall of each tube will be formed to contact the sidewall of an adjacent tube. In other embodiments, both sidewalls will be formed. Our invention contemplates alternate methods of forming the sidewalls of the tubes. The sidewalls can be formed during fabrication of a tube half, after the tubes are fabricated but not yet assembled into the radiator core, or after the tubes are assembled into the core, as may be required or preferred by those constructing a radiator according to our invention.
These and other forms, aspects, advantages, and novel features of our invention will be readily apparent upon consideration of the following drawings and detailed description of exemplary and preferred embodiments.